One box, not five
Inverter, solar charge controller, AC charger, breakers and displays come pre-wired inside one cabinet. You don't need a wall of separate components or a separate battery room.
FES-20 Outdoor Power Cabinet
A whole-home power plant in one weatherproof cabinet.
A 20 kW split-phase inverter, 21 kW of MPPT solar charging and a 14 kW AC charger, all in one outdoor enclosure. It's built to run directly on used Tesla Model 3 and Model X battery packs at 400 V.
- 20kW120/240V split-phase output
- 21kWMPPT solar input, up to 700 VDC
- 14kWAC / generator charger
- 400VTesla pack DC bus
Lives outside
An IP54 steel enclosure with a rain hood, gasketed locking door and filtered fan cooling. Our units have been running outdoors under the array since 2023.
Runs on used Tesla packs
The DC bus is native 400 V, the same voltage as a Tesla Model 3 or Model X pack. There's no repacking or DC-DC converter in between, and a 75–100 kWh pack connects directly.
Built for real loads
A low-frequency isolation transformer and 150% surge capacity start well pumps, compressors, shop tools and HVAC that would trip a lighter high-frequency inverter.
Show & Tell
Open the door. Everything's right there.
Tap a numbered marker to see what each part of the front panel does.
-
Weather hood & IP54 enclosure
A powder-coated steel cabinet with an overhanging rain hood keeps water off the door seam. It sits on a pad, a skid or casters.
-
21 kW MPPT solar charge controller
Takes high-voltage PV strings up to 700 VDC and charges the 400 V pack directly. A color display shows array voltage, current, power and daily harvest.
-
14 kW AC charging module
Charges the pack from grid power or a generator. On a cloudy week, a generator can put meaningful energy back into the pack quickly.
-
Charger display
Shows charging state, DC bus voltage and current, and lets you set charge limits for the pack chemistry.
-
Inverter display & keypad
Shows output voltage and frequency on each leg, load in kW, AC input status and fault codes. Settings are adjusted from the front panel.
-
Front-panel breakers
Each power path has its own labeled breaker: PV input, battery, AC output, AC input and DC loads. Any subsystem can be isolated in seconds.
-
Field-wiring terminal block
One clearly labeled terminal strip for battery, PV, AC input and the L1/L2/N output to your panel. Cables enter from below through sealed glands.
-
Filtered fan cooling
Louvered intake in the door with temperature-controlled fans. Rated to operate from −4 °F to 122 °F.
How it works
Two ways to charge, one 400 V battery, one clean output.
Solar arrayup to 21 kW · 700 VDC
Grid / Generator240 VAC input
FES-20 Cabinet
MPPTAC Charger
400 V DC bus
20 kW Inverter + LF Transformer
Used Tesla packModel 3 / Model X · ~350 V nominal
Your main panel120/240 V split-phase, 60 Hz
Why 400 V Tesla packs
The cheapest high-quality kWh are already sitting in salvage yards.
Wrecked and retired Model 3 and Model X vehicles leave behind battery packs with tens of thousands of miles of life left in them. These are liquid-thermal-managed automotive packs, often 75–100 kWh each, and they cost a fraction of new stationary storage.
Most off-grid gear runs at 48 V, which means a Tesla pack has to be torn down and rebuilt before it can be used. The FES-20 skips that step. It's designed around the pack's native ~400 V system, so the pack stays sealed and intact.
- About 1/8th the current of a 48 V system at the same power, so you get thinner cable, less heat and less loss.
- No teardown. Modules, busbars and cooling plates stay as Tesla built them.
- Freedom Battery Interface. Our controller talks directly to the pack's built-in battery management system and puts it on your phone. See the dashboard →
Runtime estimator
Assumes a 90% usable window and ~93% inverter efficiency. A typical U.S. home averages about 1.2–1.5 kW.
Usable energy–
Runtime at this load–
Battery current at 400 V–
Same load on a 48 V system–
Freedom Battery Interface
Know exactly what your battery is doing.
A used Tesla pack shouldn't be a mystery box. The Freedom Battery Interface connects to the pack's own brain, the Tesla battery management system, and puts everything it knows on a simple web page. Pull it up on your phone from the kitchen table.
The big picture, at a glance
How full is the battery? How many kWh are left? Is power coming in from the panels or going out to the house? The Overview answers all of it in about a second.
The fuel gauge shows state of charge. The power dial swings right when you're charging and left when you're using power. The side panel shows the limits the pack itself reports, so you always know how hard you can push it.
- Charge level and kWh left, straight from the pack
- Charging or discharging, in kW, live
- Temperatures, voltage and health in one place
- Lifetime energy in and out
All 96 cell groups, side by side
A Model 3 pack is built from 96 groups of cells connected in a chain, and a battery is only as good as its weakest group. The Cells page shows every one of them.
Healthy groups line up like a picket fence. One that's drifting low sticks out right away, like #42 in blue here. Catching that early can be the difference between a simple fix and a dead pack.
Safety you set once and forget
The interface runs the pack's contactors, the heavy-duty relays that connect the battery to the cabinet. It won't close them unless the pack is talking, its safety loop is intact and every limit is in range.
If any cell group goes too low or too high, or the pack gets too hot, it disconnects the battery on its own. You choose the thresholds; ours ship at 3.00 V, 4.20 V and 55 °C.
Check a pack before you buy
Listen-only mode reads a pack without ever switching it on, so you can see its cells and capacity before you commit.
Updates over WiFi
New features install wirelessly, with no laptop trip to the shed. Updates are blocked while the battery is connected.
Password protected
Your dashboard sits behind a login, so only you can see the controls or change settings.
Keeps a diary
An event log and downloadable data history show what the pack has been doing while you were away.
Screenshots from the live dashboard running in demo mode.
Specifications
FES-20 technical data
Typical configuration. Final settings are matched to your battery and array at order time.
Inverter output
- Continuous power
- 20 kW
- Surge
- 150% (30 kW) for 10 s
- Output
- 120/240 VAC split-phase (L1 / L2 / N)
- Frequency
- 60 Hz ±0.05 Hz
- Waveform
- Pure sine, THD ≤3% (linear load)
- Dynamic response
- ≤5% deviation, ≤50 ms (0–100% step)
- Topology
- IGBT / SVPWM with low-frequency isolation transformer
- Peak efficiency
- Up to 94%
Solar charging
- Array capacity
- 21 kW
- Charge control
- MPPT
- Max PV input voltage
- 700 VDC
- Charge profile
- Programmable bulk / absorb / float for lithium chemistry
- Display
- Color LCD: PV V / A / W, energy harvested
AC input & charging
- AC charger
- 14 kW integrated AC–DC module
- AC input
- 240 VAC grid or generator
- Operating modes
- Battery / solar priority or AC priority
- Transfer
- AC input pass-through to loads
- Generator start
- Dry-contact auto start (optional)
Battery
- DC bus
- 400 V class
- Designed for
- Tesla Model 3 & Model X packs (96-series)
- Also supports
- Other 400 V-class lithium banks by arrangement
- Pack management
- Freedom Battery Interface: WiFi dashboard, 96-group cell monitoring, automatic contactor protection
- Protection
- Reverse polarity, under/over-voltage, over-current, short circuit, over-temperature
Monitoring & control
- Displays
- Solar controller, charger and inverter screens
- Communications
- RS485 / Modbus
- Disconnects
- Front-panel PV input, battery, AC output, AC input & DC loads breakers
- Indicators
- LCD + LED status and fault codes
Enclosure & environment
- Rating
- IP54 outdoor
- Construction
- Powder-coated steel, rain hood, lockable gasketed door
- Cooling
- Temperature-controlled fans, filtered louvers
- Operating temp
- −20 to +50 °C (−4 to 122 °F)
- Humidity
- 0–95% non-condensing
- Altitude
- ≤3000 m (derate above 1000 m)
- Noise
- ≤60 dB at 1 m
- Cable entry
- Bottom, through sealed glands
Specifications subject to change. High-voltage DC systems must be installed by a qualified electrician in accordance with local code.
In the field since 2022
Not a render. Four years of real sun and weather.
Every photo here comes from a real install on a working homestead.
Who it's for
Built for people who want their power on their own terms.
Off-grid homesteads
Full 120/240 V service for the whole house, the well and the shop, with no utility in the picture.
Rural backup
Keep the lights, freezer and well running through multi-day outages, with generator charging as a backstop.
Shops & barns
Low-frequency transformer muscle for compressors, welders, saws and pumps.
Cabins & remote sites
One outdoor cabinet and one sealed pack. There's no battery room to build and no wall of gear to fit inside.
EV-pack tinkerers
Finally a turnkey home for that salvage Model 3 or Model X pack sitting in the garage.
Installers
A repeatable, single-cabinet system that's quicker to wire and easier to explain to customers.
FAQ
Common questions
Is this grid-tied? Will it sell power back to the utility?
No. The FES-20 is an off-grid / backup power center. Grid power or a generator can connect to the AC input to charge the battery and pass power through to your loads, but the cabinet does not export energy to the utility.
Which Tesla packs work?
The system is designed around the 96-series ~400 V packs used in the Tesla Model 3 and Model X. Other 400 V-class lithium batteries can be accommodated by arrangement. Tell us what you have and we'll confirm compatibility.
Do I have to open up or rebuild the pack?
No. The pack stays sealed. Power connects through the pack's high-voltage connection, and the Freedom Battery Interface connects to its low-voltage harness to monitor and manage it.
Can I check on my battery from my phone?
Yes. The Freedom Battery Interface joins your home WiFi and serves a password-protected dashboard to any phone, tablet or computer. It shows charge level, kWh left, power in and out, temperatures and every cell group, and it lets you adjust the safety limits.
Can it start a well pump or air conditioner?
Yes. That's what the low-frequency isolation transformer is for. The inverter handles 150% of rated output for 10 seconds, which covers the inrush of typical deep-well pumps, compressors and HVAC equipment within its 20 kW rating.
Can it really live outside year-round?
Yes. The cabinet is IP54-rated, with a rain hood, gasketed door and fan cooling, and is rated from −4 °F to 122 °F. The units in our photos have run outdoors under the array since mid-2023.
How much solar can I connect?
Up to 21 kW of PV through the built-in MPPT controller, with strings up to 700 VDC. We'll help you lay out strings so their cold-weather open-circuit voltage stays under that limit for your panels and climate.
Who installs it?
This is a high-voltage DC system and should be installed by a qualified electrician to local code. We provide wiring documentation and work with your installer.
What does it cost and how long does it take?
Pricing and lead time depend on configuration and current build schedule. Send a quote request and we'll get back to you with current numbers.
Get a Quote
Let's power your place.
Tell us about your property, your loads and the battery you have or plan to buy. We'll get back to you with a configuration and price.